The present invention relates to an improved electro-magnetic fluid pump, and more particularly relates to improvement in supporting construction for a reciprocating piston assembly in an electro-magnetic fluid pump such as an air pump in which the piston assembly is alternately driven for movement in one axial direction by magnetic attraction and for movement in the other axial direction by spring repulsion.
The electro-magnetic fluid pump of the above-described type is in general provided with a stator core connected to a given electric power source and a piston assembly carrying an armature. As the stator core is excited, magnetic attraction by the stator core acts on the armature to drive the piston assembly for movement in one axial direction of the pump while overcoming the spring repulsion and resultant lowering in pneumatic pressure caused by increase in volume of a piston chamber admits introduction of the fluid into the piston chamber via one check valve placed in the open state. As the stator core is de-excited due to operation of a rectifier interposed between the stator core and the electric power source, the magnetic attraction disappears the spring repulsion urges the piston assembly on movement in the other axial direction of the pump. Resultant rising in the pressure caused by reduction in volume of the piston chamber admits discharge of the fluid out of the piston chamber via the other check valve placed in the open state. Repeated excitement and de-excitement of the stator core enables the fluid pump to supply the fluid in a cyclic fashion.
With the supporting construction for the piston assembly, in the conventional electro-magnetic fluid pump, the piston assembly is liable to be biased towards either of the magnet poles of the stator core during its reciprocal movement due to the magnetic attraction acting on the armature it carries. This biased magnetic attraction greatly hinders smooth reciprocal movement of the piston assembly, thereby causing serious biased abrasion of its parts which leads to short life of the fluid pump.
In addition to the foregoing disadvantage, the mechanical spring used in the conventional fluid pump tends to assume an off-center biased posture during its compression and recovery from the compression. As the movement of the piston assembly is partly under control of this spring repulsion, the biased posture of the spring often causes biased movement of the piston assembly in a more or less amplified fashion. This undoubtedly accelerates abrasion fatique of the piston assembly and its related parts of the fluid pump.
The stator core usually includes a pair of coil windings mounted to its sections providing the magnet poles. In order to apply uniform magnetic attraction to the armature on the reciprocating piston assembly, the coil windings need to be always maintained at correct positions on the above-described sections. However in practice, vibrations caused by furious reciprocation of the piston assembly tend to cause unexpected displacement of the coil windings on the associated sections. Such displacement of the coil windings naturally causes corresponding disorder in the magnetic attraction acting on the armature on the piston assembly, thereby increasing biased abrasion of the piston assembly and its related parts of the fluid pump.
The piston reciprocates in the piston cylinder with the outer surface of the former in sliding frictional contact with the inner wall of the latter. Since the reciprocation of the piston in the piston cylinder is extremely fast, the piston must generally have a large diameter in order to remain reliably accommodated in the piston cylinder, especially when the magnetic induction field acting on the piston armature is biased in the above described manner. The large area of engagement between the piston and the piston cylinder results in great frictional losses.